1993 рік

Film specimens and blend fibres of poly(p-phenylene 1,3,4-oxadiazole) (p-PODZ) and poly(p-phenylene terephthalamide) (PPTA) have been prepared. Morphologies were studied by optical and electron microscopy. Transparent films could be coagulated from ternary solutions under conditions that prevent large-scale phase separation while morphologies change in blend fibres with composition. A fibril matrix morphology is formed at low PPTA contents. Co-continuous morphologies result when the PPTA fraction increases and, finally, p-PODZ is spherically dispersed in PPTA. The mechanical behaviour has been examined using stress-strain and drawing experiments. The modulus of elasticity increases strongly when small amounts of PPTA are added to p-PODZ. The results are discussed in terms of the Halpin-Tsai model.

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We report the chemical synthesis of an N-substituted water-soluble polyaniline derivative. This novel processable conducting polymer has been characterized by a wide range of techniques including visible absorption, FTi.r. and 1H n.m.r, spectroscopy, scanning electron microscopy, cyclic voltammetry in non-aqueous media, room temperature d.c. conductivity measurements, photon correlation spectroscopy and thermogravimetry.

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In order to improve oil and water repellency, amino-terminated poly(dimethylsiloxane)s were blended in an epoxy resin. It was hypothesized that the low surface energy poly(dimethylsiloxane) segment will absorb and orient to the exterior of the resin to make a thin surface film. Results from an ESCA investigation showed that both the amount of Si2p and Ols in the modified resin surface increased with an increase in the modifier content, and reached 0.5. Both advancing and receding contact angles for an aluminium plate coated with modified resin dipping into and out of water and dimethylphthalate increased by the addition of these modifiers. The peel strength of a pressure-sensitive adhesive affixed to the modified epoxy resin decreased dramatically.

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Several fluorinated aromatic amic acid and imide model compounds and their intermediates were prepared and investigated in N-methylpyrrolidinone by 19F and 13 C n.m.r. Starting materials included 4-fluoroaniline, 3-fluorophthalic anhydride, 2,2-bis(3,4-carboxyphenyl)hexafluoropropane dianhydride and 2,2-bis(4- aminophenyl)hexafluoropropane. The advantages of 19F n.m.r, for studying amic acid and imide chemistry were numerous. Anhydride and amine starting materials, as well as amic acid, isoimide and imide compounds, were easily identified in the 19F n.m.r, spectra. Isomeric contents of amic acid mixtures were directly measurable. Many unique aspects of polyimide chemistry, such as amic acid equilibria and imide interchange reactions, could be quantitatively identified. Data from 13C n.m.r, and 19F n.m.r, were related in many cases, as were the carbon-fluorine coupling constants.

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Dynamic mechanical, tensile and impact properties and modes of failure of binary blends of polypropylene and ethylene-propylene random copolymer rubber (PP/EPR) were studied over a wide interval of EPR volume fractions. The effect of grafting maleic anhydride on both PP and EPR on the mechanical properties was also investigated. The effects of elastomer inclusions on the failure processes were analysed in terms of critical strain energy release rate and Charpy notched impact strength (NIS). Phase morphology of the blends was examined using dynamic mechanical spectroscopy and SEM. PP remains as a continuous phase even as a minor component. This is reflected by the experimental values of elastic moduli significantly higher than those predicted using the Kerner model. The plane strain and plane stress limits of the critical strain energy release rate for initiation of cracks in the blends were the same as those for neat PP. On the other hand, the presence of EPR decreased the yield strength of the material due to the overlapping stress fields of adjacent particles, thereby increasing significantly the critical strain energy release rate for crack propagation. This was reflected by an increase in NIS. The results are explained in terms of a mixed mode of fracture with macroscopic transition from the state of plane strain to plane stress.

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High-quality polypyrrole membranes have been made by an electrochemical method. These membranes were robust and had a high conductivity (typically 60 S cm- 1 ). Investigations into the transport properties of these membranes using copper (1I) as the transporting species demonstrated the use of applied potential to control the rate of transport. Differences of two orders of magnitude in the permeability of copper across the membrane were found.

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The use of ultra high molecular weight polyethylene (UHMW-PE) fibres in composite materials is limited by their poor adhesion to the matrices. The wetting of the fibre is an integral step in the adhesion process but the extent of fibre wetting is often difficult to establish. Both surface roughness and surface polarity contribute to fibre wettability. A flotation method has been used to study the wettability of chemically etched UHMW-PE fibres. The flotation is defined by the percentage of fibres that float on a liquid flotation medium. The dependence of flotation on surface tension exhibits a float/sink transition that can be used to characterize the effects of surface roughness and surface oxidation. Chromic acid removes an oxygen-rich skin on the as-received fibre surface, increases surface roughness and oxidizes the UHMW PE yielding an increase in apparent surface tension.

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Ultra-drawing behaviour in the gel-like spherulite press method has been investigated using two kinds of gel-like spherulites formed from 1.0 and 2.0wt% solutions of ultra-high-molecular-weight polyethylene. The influence of chain entanglement density in a solution on the increase in strength and modulus with ultra-drawing is discussed. An equation predicting the maximum draw ratio from the drawing stress of the predrawn specimens is presented. It is concluded that the influence on the ultra-drawing behaviour of the spherulite size and lack of chain connection between spherulites can be ignored in this processing method.

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A series of three-point bend fracture toughness tests was performed at various loading rates and temperatures on both rubber-modified and unmodified epoxy specimens. The fracture toughness of the modified samples was determined to be rate- and temperature-dependent. Using time temperature superposition, an apparent activation energy was determined by shifting the fracture toughness data along the rate axis for each temperature tested. Surprisingly, this apparent activation energy calculated for the rubber-modified epoxy was found to be within 2% of the value of the activation energy determined for the /~ relaxation peak found from small strain d.m.a, measurements of the unmodified epoxy matrix. This was an unexpected yet interesting correlation. Since shear yielding is the primary mechanism by which this epoxy system is toughened, it can be hypothesized the/~ relaxation may significantly influence the kinetics of yielding and consequently the fracture tougness of the material. Plastic zone geometry and fracture mechanisms were investigated and were found to support this hypothesis

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Macroporous beaded polymers of varying pore sizes were synthesized coated with polyethyleneimine and derivatized with glutaraldehyde to generate aldehyde pendant groups. Penicillin G acylase (EC 3.5.1.11) was immobilized by covalent binding and the performance of immobilized enzyme was evaluated in batch mode. The expression was estimated as 43%. The shift in pH optima was marginal. The optimum temperature shifted from 40 to 57°C and Km shifted from 31 to 12.8/~mol. Immobilization enhanced the thermal stability of the enzyme.

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